Field
This invention relates generally to a waveguide iris bandpass filter and, more particularly, to a waveguide iris bandpass filter block that includes compressible ribbon strips positioned on opposing sides and adjacent to an iris filter formed in the block between split halves of the block, where the strips change an “a” dimension of the iris filter so as to increase the iris openings and provide filter tuning.
Discussion
Many electronic data and communications systems employ filters for filtering both transmit and receive signals so as to only pass signals within a particular frequency band of interest. One type of bandpass filter is known as a waveguide iris bandpass filter that includes a plurality of waveguide cavity sections separated by a conductive iris configured transverse to the waveguide aperture, where the iris causes a discontinuity in the propagation of the signal by generating a shunt reactance that rejects signals outside of the frequency band of interest. The iris perturbs the electromagnetic field of the propagating wave, and its size sets the frequency band of interest and the signal return loss. A typical waveguide iris filter is defined by the number of poles that it has, where each cavity section represents a pole, and the higher the number of poles the greater the rejection of frequencies outside the frequency band of interest.
As the frequency band of interest increases the size of the waveguide of a bandpass filter decreases. As a result of machine tolerances, high frequency waveguide iris filters cannot be perfectly machined to the specific frequency band of interest. Tuning screws can be employed in waveguide iris filters to perturb the electromagnetic field of the signal so that the filter is better tuned to the desired frequency band. However, at frequency bands in the terahertz frequency range, where the waveguide dimensions are extremely small, not only do the machine tolerances have a strong impact on the filter performance, but the tuning screws become too large to provide the desired frequency tuning.